Means to vary the intensity of illumination of electroluminescent display segments

ABSTRACT

Means for controlling an alternating current selectively applied to energize a plurality of electroluminescent segments so as to vary the intensity of illumination of the selectively energized electroluminescent display segments.

United States Patent Inventors Robert J. Molnar New York, N.Y.;

Walter Pariomak, Wallington, NJ. Appl. No. 758,378 Filed Sept. 9, 1968Division of Ser. No. 535,745, Mar. 21, 1966, Pat. No. 3,440,637

Patented Apr. 6, 1971 Assignee The Bendix Corporation MEANS TO VARY THEINTENSITY OF ILLUMINATION OF ELECTROLUMINESCENT DISPLAY SEGMENTS PrimaryExaminer-John W. Caldwell Assistant Examiner-Marshall M. CurtisAttorneys-Herbert L. Davis and Plante, Hartz, Smith and Thompsonsclmmsdnmwmg Flgs' ABSTRACT: Means for controllin an altematin current gg US. Cl 340/324, selectively applied to energize a plurality ofelectrolu- 315/169, 340/335 minescent se ents so as to vary the intensitof illumination y Int. Cl 601d 7/00, of the selectively energizedelectroluminescent display seg- G09b 9/32 ments.

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PATENTED APR 6 |97| SHEET 1 UF 3 MEANS TO VARY THE INTENSITY OFILLUMINATION OF ELECTROLUMINESCENT DISPLAY SEGMENTS CROSS-REFERENCE TORELATED APPLICATIONS The present application is a division of acopending U.S. application Ser. No. 535,745, filed Mar. 21, 1966, andnow U.S. Pat. No. 3,440,637 granted Apr. 22, 1969 to Robert J. Molnarand Walter Parfomak for a Solid State Display with Electronic DriveCircuitry.

The present invention is directed to a means to vary the intensitive ofillumination of a plurality of selectively illuminatedelectroluminescent display segments as described and claimed herein withreference to the dimming control of FIG. 4. The pulse responsive controlnetwork described herein is the subject matter of a U.S. applicationSer. No. 758,946 filed Sept. 11, 1968 by Robert J. Molnar and WalterParfomak as another division of the U.S. application Ser. No. 535,745filed Mar. 21, 1966, and which last mentioned application was in turnfiled as a continuation-in-part as to all common subject matter of a nowabandoned U.S. application Ser. No. 467,391, filed Jun. 28, 1965 byRobert J. Molnar and Walter Parfomak for a Solid State Display withElectronic Drive Circuitry.

The solid state display system to which the present invention may beapplied may include a condition sensor, comparator, drive circuitry,driven step integrator network and feedback summation network fordriving a plurality of electroluminescent display segments.

In such a display system the condition sensor may, for example, include:1 a thermocouple of a type arranged to provide an analog direct currentsignal corresponding to a sensed temperature condition; or- (2) thecondition sensor may be of a fuel flow synchro sensing type which maynecessitate the use of a converter such as described and claimed in aU.S. Pat. No. 3,375,508, granted Mar. 26, 1968, to Robert .I. Molnar andWalter Parfomak, the inventors of the present invention.

Further, the comparator provided in the system may be of a typedescribed and claimed in a U.S. Pat. No. 3,363,l 12 granted Jan. 9,1968, to Robert J. Molnar and Walter Parfomak, the inventors of thepresent invention.

Moreover, the electronic drive circuitry utilized in the system may beof a type described and claimed in a U.S. Pat. No. 3,333,114 grantedJul. 25, 1967, to Robert J. Molnar and Walter Parfomak, the inventors ofthe present invention.

Furthermore, there may be provided in the drive circuitry a controlcircuit and electronic step integrator of a type described and claimedin a U.S. Pat. No. 3,427,609 granted Feb. 11, 1969 on a copending U.S.application Ser. No. 41 1,803, filed Nov. 17, 1964 by Robert J. Molnarand Walter Parfomak, the inventors of the present invention. All of theforegoing applications and patents have been assigned to The BendixCorporation, the assignee of the present invention.

As distinguished from the foregoing features, the present invention isdirected to a means for adjusting an alternating current for energizingthe plurality of electroluminescent display segments so as to vary theintensity of illumination of the display segments as more specificallydescribed and claimed herein with reference to FIG. 4.

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention isin the field of solid state display with electronic drive circuitry and,more particularly, to an improved control network including means foradjusting an alternating current for energizing a plurality ofselectively illuminated electroluminescent display segments so as tovary the intensity of illumination thereof.

2. Description of the Prior Art Heretofore, solid state display systemshave been provided including means for controlling the illumination of astack of electroluminescent segments which may be of a type similar tothat of the electroluminescent segments disclosed in a U.S. Reissue Pat.No. 26,207, granted May 23, 1967 to Frederick Blancke Sylvander andassigned to The Bendix Corporation, assignee of the present invention.

In the display system of the U.S. Reissue Pat. No. 26,207, and in thearrangement of the present invention, the electroluminescent segmentsare of a type having thin films of phosphor material sandwiched orpositioned immediately between two electrical conductive layers one orboth of which may be transparent. 1n such an arrangement, eachelectroluminescent layer is essentially a capacitor which is so arrangedthat upon the application of an alternating current voltage across theouter conductive layers, the phosphor material will emit light, asheretofore explained in the aforenoted U.S. Reissue Pat. No. 26,207,while upon a direct current voltage being applied thereto, the capacitoreffect of the electroluminescent segment serves to block the passage ofthe direct current therethrough so that no light is emitted from suchelectroluminescent segment.

In the present invention, the specific control network for the stack ofelectroluminescent display segments is quite different from thatdisclosed in the U.S. Reissue Pat. No. 26,207, in that in addition tothe provision of a means responsive to an output signal proportional toa sensed condition to selectively operate a control network so as toconnect a source of alternating current to said display segments toeffectively illuminate said segments so as to provide a variable lengthluminous display column indicative of the sensed condition, there isfurther provided in the present invention an operatoroperative means, asshown fails detail by FIG. 4, for adjusting the alternating current fromsaid source so as to vary the intensity of the illumination of theelectroluminescent display segments and thereby enable the operator tobetter distinguish the variable length display column under differentoperating conditions of ambient illumination. The prior art fails tosuggest the simplified control network of the present invention foradjusting the alternating current so as to vary the intensity of theillumination of the plurality of electroluminescent display segmentsselectively connected thereto through the control network.

SUMMARY OF THE INVENTION The invention contemplates an improved networkfrom controlling the intensity of illumination of a stack ofelectroluminescent display segments selectively energized from a sourceof alternating current.

Another object of the invention is to provide a means for controllingthe illumination of a stack of electroluminescent display segmentsincluding a back biased diode bridge network in series with a source ofalternating current, and means for effecting selective energization ofthe segments, together with a variable direct current supply voltage toback bias the diode bridge so as to control the effective alternatingcurrent applied across opposite conductive layers of the stack ofelectroluminescent segments to in turn vary the intensity ofillumination of a luminous display column.

Another object of the invention is to provide a diode bridge networkarranged to limit the passage of alternating current therethrough so asto effect illumination of the electroluminescent display segments withonly that portion of the alternating current of a voltage greater than aback biasing direct current voltage, set by adjustment of anoperator-operative potentiometer, so as to provide a precise control ofthe intensity of illumination of the electroluminescent display columnregardless of the number of electroluminescent segments that may beselectively activated.

A further object of the invention is to provide a stack ofelectroluminescent segments connected in series with a blocking diodebridge network, a source of alternating current, and means to connectthe source of alternating current through the blocking diode bridgenetwork so as to selectively illuminate the segments, the blocking diodebridge network including a control potentiometer to vary a back biasingdirect current voltage applied to the diodes of the bridge network sothat the alternating current supplied across the electroluminescentsegments may be varied to reduce or increase the brightness ofillumination of the selectively energized electroluminescent displaysegments.

These and other objects and advantages of the invention are pointed outin the following description in the terms of the embodiment thereofwhich is shown in the accompanying drawings.

IN THE DRAWINGS FIG. II shows a block diagram of an electroluminescentphotoconductor solid state display system embodying the invention.

FIG. 2 is a symbolic representation of the electroluminescentphotoconductor matrix in a novel layout arrangement for indicatingcoarse, fine, and sectional controls in driving the electroluminescentdisplay segments.

FIG. 3 shows an enlarged detailed fragmentary schematic view of theelectroluminescent photoconductor matrix shown in FIG. 2, as attached tothe electroluminescent display segments for illuminating the same.

FIG. 4 is a detailed circuitry of the dimming circuit shown in FIG. 1.

DESCRIPTION OF THE INVENTION The electroluminescent photoconductor solidstate display system comprises an indicator panel and a driven networkutilizing a novel optoelectronic approach. A condition sensor device isprovided to obtain from analog signals such as exhaust gas temperature,fuel flow or a tachometer, a direct current analog signal to control acomparator circuit and in turn an electronic drive circuitry to effect acorresponding control of a driven network including electroluminescentsegments arranged in an instrument simulating a thermometer type movingdisplay.

More specifically the condition sensor means used may, for example, be:l a thermocouple of a type arranged to provide an analog direct currentsignal corresponding to a sensed temperature condition; or (2) thecondition sensor means may be of a fuel flow synchro signal sensing typewhich may necessitate the use of a converter such as described in U.S.Pat. No. 3,375,508, granted Mar. 26, I968 to Robert .I. Molnar et al.,assigned to The Bendix Corporation, the same assignee as the presentinvention; or (3) the condition sensor means may be tachometer signalsensing means of a type in which tachometer signals are converted toproduce one pulse per cycle of a generator speed and in which theamplitude and width of the pulses are controlled so that a filteredoutput produces a direct current analog signal which is an accuratefunction of the sensed condition or tachometer speed.

Referring to the drawing of FIG. 1, there is indicated a block diagramof the system. A condition sensor 210 provides a direct current analogsignal corresponding to the sensed condition which is directed, as shownby arrow 21], to an electronic error detector, such as, a comparator216, which may be analogous to a differential in an electromechanicalsystem. The comparator 216 may be of the type described and claimed inthe aforenoted U.S. Pat. No. 3,363,I I2, granted Jan. 9, I968 to RobertJ. Molnar and Walter Parfomak for a single transistorized comparatorcircuit and assigned to The Bendix Corporation, the assignee of thepresent invention.

An electronic drive circuitry 218 which may be of a type described andclaimed in the aforenoted U.S. Pat. No. 3,333,I I4, granted .Iul.25,l967 to Robert Molnar and Walter Parfomak for an electronic drivecircuit and assigned to The Bendix Corporation, may include as shown byFIG. 5, a control circuit 219 which receives the differential outputsignal, as shown by arrow 215, from the comparator 216. The controlcircuit 219 in turn controls the operation of the drive circuit 218 inapplying driving pulses, as shown by arrow 217 of FIG. 1, to a drivennetwork 221.

The driven network 221, under control of the driving pulses applieselectrical pulses, as indicated by the arrow 223 of FIG. 1, to regulatethe operation of the electroluminescent matrix 220. Further, a summationnetwork 222 receives electrical signal information, as shown by arrow225, from the driven network 221 and directs a feedback signal, asindicated by the arrow 227, to the comparator 218 corresponding to theregulated condition of the matrix 220.

More specifically, as described and claimed in the aforenoted U.S. Pat.No. 3,440,637; the driven network 221 directs signal informationcorresponding to the regulated operation of the electroluminescentcapacitor strips extending along the X axis and Y axis of the matrix220, while the summation network 222 then integrates the informationsignal until the direct current feedback signal voltage directed to thecomparator 216 from the summation network 222, as shown by an arrow 227of FIG. 1, is equal to the direct current analog signal voltage directedto the comparator 216 from the condition sensor 210, as shown by thearrow 221. That is, the DC feedback signal voltage acts in opposition tothe DC analog signal voltage so that when the resulting differential orerror signal voltage is reduced to zero, the integration isaccomplished.

Electroluminescent Matrix It should be also noted at this time that, asdescribed and claimed in the U.S. Pat. No. 3,440,637, the multisegmentswitching of the electroluminescent display portion of the inventionrequires three orders of control including a fine control, a coarsecontrol, and a third order of control achieved by photoconductorswitches 224 being arranged to receive light from the electroluminescentcapacitor strips F1 to F10 of the electroluminescent matrix 220, asshown by arrows '229 of FIG. 1.

A last row of Y axis extending photocells are provided to control theexcitation of each succeeding row of X axis extending photocells inwhich the first row of X axis extending photocells does not require suchcontrol since it is excited continuously.

The electroluminescent matrix 220 of FIG. 1 is shown symbolically inFIG. 2, partially in schematic form in FIG. 3 and in detail in the U.S.Pat. No. 3,440,637.

In addition, the photoconductor switches 224, shown in the block diagramof FIG. 1, are also shown symbolically in FIG. 2, partially in FIGS. 3and 4, and indetail in the U.S. Pat. No. 3,440,637.

An electroluminescent display column made up of a series ofelectroluminescent display segments 226, shown in FIG. 1, is connectedto be energized by the electroluminescent matrix 220 and thephotoconductor switches 224, as shown by arrows 229 and 230,respectively. The electroluminescent display segments 226 are shownsymbolically in FIG. 2 and partially schematically in FIGS. 3, and 4,and in the U.S. Pat. No. 3,440,637. The electroluminescent displaysegments 226 are described more fully in the aforementioned U.S. ReissuePat. No. 26,207.

A dimming circuit 228, providing means for dimming theelectroluminescent display 226 by manual control, is shown in FIG. 1connected to the system by a line 231. The dimming circuit 228 is morespecifically shown in FIG. 4, as including a back biased diode bridge inseries with the ground leg of the electroluminescent display section, ashereinafter more fully described.

As shown symbolically in FIG. 2 and in detail in the U.S. Pat. No.3,440,637, the electroluminescent matrix 220 is optically coupled to thephotoconductor switches 224 to form an electroluminescent photoconductormatrix 234. The electroluminescent photoconductor matrix 234 may, forexample, comprise 209 photoconductor switches indicated by numerals PCIto PC209, a coarse electroluminescent control 236 including l9electroluminescent capacitor strips C1 to C19, extending along the Xaxis, a fine electroluminescent control 238 including 10electroluminescent capacitor strips F1 to F10, extending along the Yaxis with a symbolic F11 to show the last fine control, and a sectionalcontrol 240 which includes I9 sectional photoconductor switches S1 toS19, which are rendered conductive upon illumination of the ass'ociatedcoarse control electroluminescent capacitor strips C1 to C19.

The electroluminescent photoconductor matrix 234 symbolically shows, inFIG. 2, 209 squares representing the 209 photoconductor switchesproviding driving or switching means for the 209 electroluminescentdisplay segments 226 numbered ELI to EL209. It should be noted that eachphotoconductor switch PC1 to PC209 drives its correspondingly numberedelectroluminescent segment, and in this sense are correlated one to theother. It should be also noted that FIG. 2 symbolically shows at 226 anexample of 36 activated electroluminescent segments which are driven by36 photoconductor switches PC] to PC36.

The interconnection of the photoconductor switches 224 with theircorresponding electroluminescent display segments 226 is shown in moredetail in FIG. 3 wherein the electroluminescent segments 226 arecontrolled by the photoconductor switches 224 through the fineelectroluminescent switching means 238 controlled by silicon controlledrectifier switches, as described and claimed in the US. Pat. No.3,440,637, and which control the energization of the H)electroluminescent strips F1 to F10. In addition, the coarse switchingmeans 236 is controlled by other silicon controlled rectifier switcheswhich control the energization of the I) electroluminescent strips C1 toc19, as described and claimed in the U.S. Pat. No. 3,440,637

Therefore, as shown in FIG. 3, the electroluminescent photoconductormatrix 234 illuminates 209 photoconductor switches PC1 to PC209 throughthe electroluminescent strips F1 to F and C1 to C19 controlled by thesilicon controlled rectifier switches which are operatively controlledby the driven network 221.

It should be noted that FIG. 3 is a fragmentary drawing of theelectronic circuitry to show the connection between the siliconcontrolled rectifier switches energizing the electroluminescent stripsand that the US. Pat. No. 3,440,637 shows in greater detail the siliconcontrolled rectifier electronic circuitry utilized in the solid statedisplay circuitry to drive the optoelectric portion of the system. Thatis the electronic circuitry which operates to energize the 19electroluminescent coarse control strips C1 to C19 extending in the Xaxis and the 10 electroluminescent fine control strips F1 to F10extending in the Y axis of the electroluminescent photoconductor matrix234 to provide thereby two orders of control to illuminate theelectroluminescent display segments 226. However, as hereinbeforedescribed, and as shown in FIGS. 2 and 3, multisegment switching of theelectroluminescent display 226 requires three orders of control. Thisthird order of control is effected by providing photoconductor switchesS1 to S19 of the sectional control 240 each of which sectional controlswitches corresponds to one of the photoconductors such as the lastphotoconductor in each row PC11, PC22, PC33, and so on up to the lastphotoconductor PC198 located on the next to the last row ofphotoconductors. These photoconductors, PC11, PC22, PC33, and so on toPC198 corresponding to the sectional control switches S1 to S19,respectively, are the last photoconductors on each of theelectroluminescent strips extending on the X axis from C1 to C18 exceptfor the last electroluminescent strip C19. The last photoconductor PC209may be utilized as an additional section control switch in the eventmore than 209 electroluminescent display segments were to beilluminated.

In this system the photoconductors S1 to S18 of the sec tional control240 are used to control the excitation for the next row ofphotoconductors extending on the X axis. For example, as shownschematically in FIG. 3, the photoconductor PC11 corresponding to thesectional control switch S1 is used as a stand-by power switch for thesecond row of photoconductors, PC12 to PC22.

More specifically, as shown in FIG. 3, photoconductor PC11 correspondingto sectional control switch S1 is connected through line conductors 242and 250 to one terminal of a suitable source of alternating current 243.The other terminal of the source 243 is connected by a line conductor244 to a ground 245. The photoconductor PC11 is also connected by a lineconductor 246 to electroluminescent segment F111 and in turn theelectroluminescent ELll is connected to ground 245 by a common lineconductor 248. In addition, the line conductor 250 connects the row ofphotoconductors PCI to PC11. When the electroluminescent strip C1 isilluminated, light rays are directed thereby upon the photoconductorsPCI to PC11 to reduce their electrical resistance and render themconductive of electrical energy, whereupon voltage from the alternatingcurrent source 243 will be applied through photoconductor PC11corresponding to the sectional control switch S1 to the photoconductorsPC12 to PC22 through a line conductor 252. Thereafter, should the finecontrol electroluminescent strips F1 to F10 be illuminated, then thephotoconductors PC11 to PC21 would be rendered conduc' tive; or, shouldthe coarse control electroluminescent strip C2 be illuminated, then thephotoconductors PC11 to PC22 would become electrically conductive andcurrent would be directed to the electroluminescent segments EL12 toEL22 for illuminating segments of the electroluminescent display 226.That is, when the photoconductor PC11 is switched on to illuminate theeleventh electroluminescent segment EL11 through the line conductor 246,it is also effective as the sectional control switch S1 to connectthrough the line conductor 252 for stand-by the next row of X axisextending photoconductors PC12 to PC22.

Furthermore, the photoconductor PC22 is connected to the alternatingcurrent source 243 through photoconductor PC11 by the line conductor 252and should the photoconductor PC22 have been previously renderedconductive by the illumination of the coarse control strip C2, thephotoconductor PC22 then serves to effect the illumination of theelectroluminescent segment EL22 through a line conductor 254. At thesame time photoconductor PC22 is also effective as sectional controlswitch S2 to connect for stand-by the next succeeding row of X axisextending photoconductors PC23 to PC33. The photoconductor PC33, uponillumination of the coarse control strip C3, is rendered conductive toilluminate the electroluminescent segment EL33 and is thereuponeffective as sectional control switch S3 to connect for stand-by thenext succeeding row of X axis extending photoconductors PC34 to PC44,and so on until photoconductor PC198, shown by FIG. 2, becomes effectiveupon illumination of the coarse control strip C18 to connect forstand-by the last row of X axis extending photoconductors PC 199 toPC209.

The driven network 221 while utilizing only 16 silicon controlledrectifier switches may be rendered effective to drive 10 Y axisextending fine control electroluminescent strips and 19 X axis extendingcoarse control electroluminescent strips, for energizing 209electroluminescent display segments, as explained in the aforenoted US.Pat. No. 3,440,637.

As shown schematically in FIG. 3, the electroluminescent displaysegments 226 are divided into a column of a number of small segments ofa phosphor material. The number needed being determined by the accuracy,resolution, and sensitivity requirements of the display instrument.

Dimming Control Referring now to the dimming control 228, a dimmingpotentiometer control 255 shown in FIG. 4 provides for manual control ofthe brightness of the energized electroluminescent display segments 226so that the display may be distinguishable under any condition ofambient illumination.

The dimming circuit 228, shown in FIG. 4, comprises a back biasing diodebridge rectifier 256 connected in the common conductor 231 leading fromthe display segments 226, shown in FIG. 3, and interposed between theelectroluminescent display segments 226 and the conductor 248 leading toground 245. A dimming potentiometer control 255 is provided for the areasource lamp to balance the display for darkness operation. Thebrightness of the electroluminescent segments will be adequate forvisibility in normal lighting (approximately 50 foot-candles). Thearrangement is such that the diode bridge rectifier 256 serves to limitthe passage of alternating current from the source 243 and through thedisplay segments 226 to a voltage greater than a back biasing directcurrent voltage 257 set by adjustment of the potentiometer 255. In thismanner, there is provided a precise control of the electroluminescentdisplay brightness regardless of the number of electroluminescentsegments activated.

Referring particularly -to the back biasing diode bridge rectifier 256,it will be seen that a first diode 258 comprises an anode 259 connectedto a junction 273 and thereby to the ground 245 by conductor 248 and acathode 260 connected to a junction 261 to which leads the conductor 274from the control potentiometer 255. A second diode 262 comprises ananode 263 connected to a junction 264 to which leads the line conductor231 from the electroluminescent display segments 226 and a cathode 265connected to the junction 261.

In addition, the bridge rectifier 256 comprises a third diode 266 havingan anode 267 connected to a junction 268 from which leads the conductor275 to the control potentiometer 255 and a cathode 269 connected to thejunction 264 to which leads the line conductor 231 from theelectroluminescent dis- 7 play segments 226. A fourth diode 270 has ananode 271 connected to the junction 268 and a cathode 272 connected tothe junction 273 and thereby through the common line conductor 248 tothe ground 245 In this manner, the back biasing diode bridge 256 isconnected to the ground 245 in series with the electroluminescentdisplay segments 226 by its two junctions 264 and 273. The bridgerectifier 256 is also connected to the back biasing direct currentvoltage 257 at its junctions 261 and 268 through line conductors 274 and275, respectively. The line conductor 275 is connected to a negativeterminal 276 of a direct current supply voltage 280 and to one terminal281 of a resistor 282 at junction 283. The other line conductor 274 isconnected through a movable contact arm 284 to the resistor 282 whichresistor is connected at an opposite terminal 286 to a positive terminal288 of the supply voltage 280. The lighting intensity may be adjusted,as desired, by suitable adjustment of the dimming potentiometer control255 to set the back biasing DC voltage so as to limit the effectivevoltage of the energizing alternating current applied through the bridgerectifier 256 to the electroluminescent display segments 226.

The electroluminescent display segments ELI to EL209 are essentiallycapacitors and if a direct current voltage is applied across anelectroluminescent segment no light would be produced. At the same time,if a portion of the alternate current voltage which is applied acrossthe electroluminescent segment is blocked, it will vary its brightness.Therefore, since the electroluminescent segments 226 are in series withthe bridge rectifier 256, an operator may adjust the controlpotentiometer 255 to vary the back biasing direct current, whereupon thealternating current supplied across the electroluminescent segments 226will be varied to reduce or increase the brightness of theelectroluminescent display lamps.

The alternating current activating circuit for the selectivelyilluminated electroluminescent display segments 226 may be readilytraced from the source of aLtemating current 243. Thus upon a positivehalf wave of alternating current being applied from the source 243through the conductor 244 leading to the ground 245, the positive halfwave of alternating current will be applied through the groundedconductor 248 to the junction 273 of the diode bridge 256 and thereby tothe anode 259 of the diode 258 and from the cathode 260 of the diode 258to the junction 261.

However, only that portion of the positive half wave of the alternatingcurrent will pass through the diode 258 to thejunction 261 whicheffectively overcomes the biasing force applied by the direct currentsource 280 to the cathode 260 of the diode 258. The resultant portion ofthe positive half wave of the alternating current applied at thejunction 261 will then be applied through the conductor 274 and theeffective part of the resistor 282 leading to the conductor 281 andthrough the conductor 275 to the junction 268 of the diode bridge 256.

Moreover, from the junction 268, the resultant portion of thealternating current is applied to the anode 267 of the diode 266 andfrom the cathode 269 of the diode 266 to the junction 264 where theresultant portion of the alternating current is applied through thecommon conductor 231 to one conductive layer of each of the selectivelyilluminated electroluminescent segments 226, while the oppositeconductive layer of each of the selectively illuminated segments 226 isconnected through a control section, as shown by FIG. 4, to the oppositethen negative terminal of the source of alternating current 243.

Similarly, upon the reoccurring opposite positive half wave beingapplied at the previously negative terminal of the source of alternatingcurrent 243, this opposite positive half wave will then be appliedthrough the aforementioned control section to one of the conductivelayers of each of the selectively illuminated segments 226, while apositive reverse flow of current will be effected from the oppositeconductive layers of each of the selectively illuminated segments 226,through the common conductor 231 to the junction 264 of the diode bridge256 and thereby to the anode 263 of the diode 262 and from the cathode265 of the diode 262 to the junction 261.

However, only that portion of the positive half wave of the alternatingcurrent will pass through the diode 262 to the junction 261 which hasefiectively overcome the back biasing force applied by the directcurrent source 280 to the cathode 265 of the diode 262. The resultantportion of the positive half wave of the alternating current applied atthe junction 261 will then be applied through the conductor 274 and theeffective part of the resistor 282 leading to the conductor 281 andthrough the conductor 275 to the junction 268 of the diode bridge 256.Moreover, from the junction 268 the resultant portion of the alternatingcurrent is applied to the anode 271 of the diode 270 and from thecathode 27 2 of the diode 270 to the junction 273 where the resultantportion of the alternating current is applied through the conductor 248to the ground 245 returning thereby through the conductor 244 to theopposite then negative terminal of the source of alternating current243.

It will be seen then that the resultant portion of the alternatingcurrent applied across the opposite conductive layers of the selectivelyilluminated electroluminescent display segments 226 is effectivelycontrolled by the back biasing direct current voltage applied by thedirect current source 280 as set by the adjustment of theoperator-operative potentiometer control 255. Thus the intensity ofillumination of the selectively illuminated electroluminescent segments226 may be effectively increased by decreasing the biasing voltageapplied by the direct current biasing source 280 while the intensity ofillumination may be effectively decreased by increasing the biasingvoltage applied by the direct current biasing source 280.

The dimming control 228, as described and claimed herein with referenceto FlG. 4, provides the subject matter of the present invention, wherebythe intensity of the illumination of the luminous column of theelectroluminescent display may be readily adjusted independently of thenumber of electroluminescent segments 226 that may be selectivelyilluminated so that the viewer may be able to better distinguish theindicator display column under varying conditions of ambientillumination.

Control System for Display Segments As herein described with referenceto FIG. 1, a direct current analog signal voltage effected by thecondition sensor 210 is compared in a comparator 216 with a feedbackvoltage applied through a summation network 222 by the driven network221 and any difference or error voltage is fed to the electronic drivecircuitry 218 to control the operation of a driven network 221 as morefully described in the US. Pat. No. 3,440,637.

Within the electronic circuitry the differential error voltage resultingfrom the comparison of the direct current analog signal voltage and thefeedback voltage is used to control the length of the lightedelectroluminescent display column 226. That is, a lighted condition iscaused to progress along the display column of the electroluminescentdisplay segments 226 by the resulting operation of the driven network221 which causes electroluminescent driving capacitor strips F1 to F10and C1 to C19 to shine upon the photoconductor switches PC to PC209 toexcite, in turn, a predetermined number of the 209 electroluminescentdisplay segments ELI to EL209 corresponding to an indicated value of thecondition sensed by the sensor 210.

Thus, by means of the direct current analog and feedback signals fromthe electronic circuit, the length of this lighted electroluminescentcolumn of the display segment 226 is continuously compared to the valueof the direct current input parameter of the sensor 210. When thelighted column of the display segments 226 has progressed to thepredetermined length indicative of the sensed condition, the switchingcircuit is operated to stop further movement or illumination of thecolumn of the display segment 226.

As hereinbefore described with reference to FIGS. 2 and 3, the variouselectroluminescent capacitor control strips F1 to F10 and C1 to C19 ofthe electroluminescent photoconductor drive circuits, internal to thedisplay indicator, are not made in the same geometrical format as thecolumn of the display segments 226. The display segments 226 may bemade, for example, of 44 electroluminescent display segments to theinch, but the electroluminescent capacitor control strips are providedwith a series of l parallel, spaced electroluminescent fine controlstrips F1 to F extending in Y-axis direction, and the other with aseries of 19 parallel spaced electroluminescent coarse control strips C1 to C19 extending perpendicular thereto in an X-axis direction. Theelectroluminescent strips are then connected to the electronic controlcircuitry, partly shown in schematic form in FIGS. 3 and 4, and morefully shown in the US. Pat. No. 3,440,637.

The various electroluminescent and photoconductor elements may bearranged on four or more thin cards, as shown in the US. Pat. No.3,440,637. These cards may be stacked and interconnected in the samemanner as if they were a single format. In addition, in simplifying theproduction of these electroluminescent photoconductor elements, thismethod may be used for troubleshooting and thus allow for change ofscale factor in the summation of signals from each card. Reliabilitytheory assigns a great importance to the proper assembly of individualelectroluminescent and photoconductor cells.

The electronic drive circuitry and driven network 221 and summationnetwork 222 performs the guiding control for the various coarse and fineelectroluminescent strips, the photoconductors and eventually theelectroluminescent display segments 226 as best shown and described inthe aforenoted U.S. Pat. No. 3,440,637.

The dimming circuit shown in FIG. 4 utilizes the capacitorcharacteristics of the electroluminescent display segments 226 so that adirect current applied across the opposite plates of the displaysegments 226 effects no illumination. At the same time, if a portion ofthe alternating current voltage of the illuminating current is blocked,the brightness of the electroluminescent display segments 226 will bevaried thereby. in the bridge circuit of FIG. 4, there is a directcurrent supplied in series with the alternating current voltage and withthe electroluminescent display segments 226 so that as the directcurrent is increased in the bridge rectifier 256, the alternatingcurrent across the electroluminescent display segments 226 will bereduced.

In summary therefore, the solid state display circuitry described hereinprovides for reduction in activating the circuitry by means of a fourdimensional control, the use of an electronic servo for greateraccuracy, and the use of means to simultaneously switch off all thephotoconductors for a faster response within the system. In addition,this system provides for a unique combination of electronic andoptoelectronic techniques in a matrix control with a multifunctionoperation of the coarse and fine control circuitries and a dual functionof a transfer circuit. Further, this system provides for a high accuracyproduced by a simple summation circuit, a unique circuit arrangement forexcitation control and level changes and a unique electronic isolationbetween control and display sections achieved by means of theelectroluminescent and photoconductor components and in addition thepresent invention provides a unique circuit for dimming theelectroluminescent display segments.

While one embodiment of the invention has been illustrated anddescribed, various changes in the fonn and relative arrangement of theparts, which will now appear to those skilled in the art may be madewithout departing from the scope of the invention. Reference is,therefore, to be had to the appended claims for a definition of thelimits of the invention.

We claim:

1. For use with a condition sensor of a type including means foreffecting an output signal proportional to a sensed condition, thecombination comprising a plurality of electrolu' minescent displaysegments including opposite capacitivetype plates, a first source ofalternating current, means response to said output signal to selectivelyconnect said source of alternating current across the oppositecapacitivetype plates of said display segments to illuminate saidsegments so as to provide a variable length luminous display indicativeof the sensed condition, a second source of direct current biasingvoltage, the means for selectively connecting said source of alternatingcurrent across the opposite capacitivetype plates of said displaysegments including first unidirectional current flow control meansconnecting one phase of said alternating current in a series opposingrelation with said direct current biasing voltage of said second source,and a second unidirectional current flow control means for connecting anopposite phase of said alternating current in an opposite seriesopposing relation with said direct current biasing voltage of saidsecond source, said second source of direct current biasing voltagebeing connected in a back biasing relation to said first and secondunidirectional current flow control means and in opposition to the firstand second phases of said alternating current applied through said firstand second unidirectional current flow control means across the oppositecapacitive-type plates of said display segments, and operatoroperativemeans for adjusting the direct current biasing voltage of said secondsource to vary intensity of illumination of the electroluminescentdisplay segments by the alternating current of said first source.

2. The combination defined by claim 1 in which the selective connectingmeans includes a bridge network, the first and unidirectional currentflow control means being arranged in opposite arms of said bridgenetwork, a first pair of input legs being connected between oppositearms of the bridge network, said first input legs being seriallyconnected in the means connecting said source of alternating currentacross the opposite capacitive-type plates of said display segments, anda second pair of input legs being connected between other opposite armsof the bridge network for connecting the second source of direct currentbiasing voltage across the first and second unidirectional current flowcontrol means in such a polarity sense as to apply an electromotiveforce in a back biasing relation to said first and second unidirectionalcurrent flow control means and acting in opposing relation to the firstsource of alternating current, and operator-operative means foradjusting the second source of direct current voltage so as to vary theelectromotive force acting in said opposing relation and thereby theintensity of the illumination of the electroluminescent display segmentsby the first source of alternating current applied through said bridgenetwork and across the opposite capacitive-type plates of said displaysegments.

3. The combination defined by claim 1 in which the selective connectingmeans includes a diode bridge means, the first unidirectional currentflow control means including a first pair of diodes connected inopposite arms of said bridge means in one like polarity sense, saidsecond unidirectional current flow control means including a second pairof diodes connected in other opposite arms of said bridge means inanother opposite polarity sense from said first pair of diodes, saidfirst and second pairs of diodes being connected in said bridge means insaid one and other polarity senses for connecting said one and otherphases of said'first source of alternating current in said seriesopposing relation to said second source of direct current voltage andacross said opposite capacitive-type plates of said display segments, anadjustable potentiometer connected across said second-source of directcurrent voltage and opera tively connected across opposite arms of thediode bridge means to apply the back biasing voltage to the first andsecond pairs of diodes of the diode bridge means to block passage of aportion of the alternating current applied through the diode bridgemeans and across the opposite capacitive-type plates of the selectivelyconnected display segments to thereby vary the intensity of illuminationof the selectively illuminated elec troluminescent display segments.

4. For use with a. condition sensor of a type including means foreffecting an output signal proportional to a sensed condition, thecombination comprising a plurality of electroluminescent displaysegments, each of said segments including opposite conductive layers, asource of alternating current, means responsive to said output signal toselectively connect said source of alternating current across theopposite conductive layers of said display segments to illuminate saidsegments so as to provide a variable length luminous display indicativeof the sensed condition, a bridge network, a first control junction onthe bridge network, the bridge network including a first pair ofunidirectional current flow control devices for permitting flow ofcurrent from the first control junction of the bridge network toopposite input-output junctions of the bridge network, a second controljunction on the bridge network, the bridge network including a secondpair of unidirectional current flow control devices for permitting flowof current to the second control junction of the bridge network from theopposite input-output junctions of the bridge network, means seriallyconnecting the opposite input-output junctions of the bridge networkbetween the source of alternating current and the means to selectivelyconnect said source of alternating current across the oppositeconductive layers of said display segments, a direct current voltagesource, means connecting the direct current voltage source across saidfirst and second control junctions in a polarity sense to back bias theunidirectional current flow control devices in opposite relation to theunidirectional flow of current therethrough by the alternating currentsource so as to block passage of at least a portion of the alternatingcurrent applied by the alternating current source and permit passagethrough the bridge network of that portion of the alternating currentwhich effectively overcomes the biasing voltage of the direct currentvoltage source and thereby control intensity of illumination of theselectively illuminated electroluminescent segments.

5. The combination defined by claim 4 including a potentiometer having aresistor element connected across said source of direct current voltage,the means connecting the direct current voltage source across said firstand second control junctions of the bridge network including anadjustably positioned control arm cooperatively arranged in relation tosaid resistor element so as to provide first and second portions of saidresistor element, each of said portions of the resistor element beingvariable relative one to the other by the positioning of the controlarm, and an operator-operative control to vary the position of thecontrol arm and the effective resistance of said portions of theresistor element relative one to the other and thereby provide avariable voltage divider permitting a variable biasing voltage to bederived and applied by the direct current voltage source across thefirst and second control junctions so that the portion of thealternating current which effectively overcomes the derived biasinvoltatge applied by the direct current voltage source may e ect a 0w ofcurrent through the second pair of unidirectional current flow controldevices to the second control junction of the bridge network and throughat least one of said portions of the resistor element of thepotentiometer to the first control junction of the bridge network andselectively through the first pair of unidirectional current flowcontrol devices to the output of alternating input-output junctions ofthe bridge network.

1. For use with a condition sensor of a type including means foreffecting an output signal proportional to a sensed conditIon, thecombination comprising a plurality of electroluminescent displaysegments including opposite capacitive-type plates, a first source ofalternating current, means response to said output signal to selectivelyconnect said source of alternating current across the oppositecapacitive-type plates of said display segments to illuminate saidsegments so as to provide a variable length luminous display indicativeof the sensed condition, a second source of direct current biasingvoltage, the means for selectively connecting said source of alternatingcurrent across the opposite capacitive-type plates of said displaysegments including first unidirectional current flow control meansconnecting one phase of said alternating current in a series opposingrelation with said direct current biasing voltage of said second source,and a second unidirectional current flow control means for connecting anopposite phase of said alternating current in an opposite seriesopposing relation with said direct current biasing voltage of saidsecond source, said second source of direct current biasing voltagebeing connected in a back biasing relation to said first and secondunidirectional current flow control means and in opposition to the firstand second phases of said alternating current applied through said firstand second unidirectional current flow control means across the oppositecapacitive-type plates of said display segments, and operator-operativemeans for adjusting the direct current biasing voltage of said secondsource to vary intensity of illumination of the electroluminescentdisplay segments by the alternating current of said first source.
 2. Thecombination defined by claim 1 in which the selective connecting meansincludes a bridge network, the first and unidirectional current flowcontrol means being arranged in opposite arms of said bridge network, afirst pair of input legs being connected between opposite arms of thebridge network, said first input legs being serially connected in themeans connecting said source of alternating current across the oppositecapacitive-type plates of said display segments, and a second pair ofinput legs being connected between other opposite arms of the bridgenetwork for connecting the second source of direct current biasingvoltage across the first and second unidirectional current flow controlmeans in such a polarity sense as to apply an electromotive force in aback biasing relation to said first and second unidirectional currentflow control means and acting in opposing relation to the first sourceof alternating current, and operator-operative means for adjusting thesecond source of direct current voltage so as to vary the electromotiveforce acting in said opposing relation and thereby the intensity of theillumination of the electroluminescent display segments by the firstsource of alternating current applied through said bridge network andacross the opposite capacitive-type plates of said display segments. 3.The combination defined by claim 1 in which the selective connectingmeans includes a diode bridge means, the first unidirectional currentflow control means including a first pair of diodes connected inopposite arms of said bridge means in one like polarity sense, saidsecond unidirectional current flow control means including a second pairof diodes connected in other opposite arms of said bridge means inanother opposite polarity sense from said first pair of diodes, saidfirst and second pairs of diodes being connected in said bridge means insaid one and other polarity senses for connecting said one and otherphases of said first source of alternating current in said seriesopposing relation to said second source of direct current voltage andacross said opposite capacitive-type plates of said display segments, anadjustable potentiometer connected across said second source of directcurrent voltage and operatively connected across opposite arms of thediode bridge means to apply the back biasing voltage to tHe first andsecond pairs of diodes of the diode bridge means to block passage of aportion of the alternating current applied through the diode bridgemeans and across the opposite capacitive-type plates of the selectivelyconnected display segments to thereby vary the intensity of illuminationof the selectively illuminated electroluminescent display segments. 4.For use with a condition sensor of a type including means for effectingan output signal proportional to a sensed condition, the combinationcomprising a plurality of electroluminescent display segments, each ofsaid segments including opposite conductive layers, a source ofalternating current, means responsive to said output signal toselectively connect said source of alternating current across theopposite conductive layers of said display segments to illuminate saidsegments so as to provide a variable length luminous display indicativeof the sensed condition, a bridge network, a first control junction onthe bridge network, the bridge network including a first pair ofunidirectional current flow control devices for permitting flow ofcurrent from the first control junction of the bridge network toopposite input-output junctions of the bridge network, a second controljunction on the bridge network, the bridge network including a secondpair of unidirectional current flow control devices for permitting flowof current to the second control junction of the bridge network from theopposite input-output junctions of the bridge network, means seriallyconnecting the opposite input-output junctions of the bridge networkbetween the source of alternating current and the means to selectivelyconnect said source of alternating current across the oppositeconductive layers of said display segments, a direct current voltagesource, means connecting the direct current voltage source across saidfirst and second control junctions in a polarity sense to back bias theunidirectional current flow control devices in opposite relation to theunidirectional flow of current therethrough by the alternating currentsource so as to block passage of at least a portion of the alternatingcurrent applied by the alternating current source and permit passagethrough the bridge network of that portion of the alternating currentwhich effectively overcomes the biasing voltage of the direct currentvoltage source and thereby control intensity of illumination of theselectively illuminated electroluminescent segments.
 5. The combinationdefined by claim 4 including a potentiometer having a resistor elementconnected across said source of direct current voltage, the meansconnecting the direct current voltage source across said first andsecond control junctions of the bridge network including an adjustablypositioned control arm cooperatively arranged in relation to saidresistor element so as to provide first and second portions of saidresistor element, each of said portions of the resistor element beingvariable relative one to the other by the positioning of the controlarm, and an operator-operative control to vary the position of thecontrol arm and the effective resistance of said portions of theresistor element relative one to the other and thereby provide avariable voltage divider permitting a variable biasing voltage to bederived and applied by the direct current voltage source across thefirst and second control junctions so that the portion of thealternating current which effectively overcomes the derived biasingvoltage applied by the direct current voltage source may effect a flowof current through the second pair of unidirectional current flowcontrol devices to the second control junction of the bridge network andthrough at least one of said portions of the resistor element of thepotentiometer to the first control junction of the bridge network andselectively through the first pair of unidirectional current flowcontrol devices to the output of alternating input-output junctions ofthe bridge network.